Field of the Invention
The present invention relates to a heat treatment technology for heating a semiconductor wafer, a glass substrate, or the like, (hereinafter, simply referred to as “substrate”) that is placed in a process chamber.
Description of the Background Art
As well known, a semiconductor component or the like is manufactured through a large number of process steps, and various manufacturing apparatuses corresponding to the respective process steps are used. Many of the apparatuses are each provided with a cleaning mechanism therein because the manufacture of the semiconductor component or the like, which is becoming finer and finer, requires an ultraclean atmosphere. For example, Japanese Patent Application Laid-Open No. 7-321046 (1995) discloses a technique that causes an ozone gas to flow under ultraviolet irradiation, to thereby remove an organic substance existing on a substrate. Japanese Patent Application Laid-Open No. 9-17705 (1997) discloses a technique in which an unnecessary film attached to a surface of an inner wall of a process chamber or to a surface of a structure inside the process chamber is cleaned away at about 200° C. with a supply of a ClF3 gas thereto. Japanese Patent Application Laid-Open No. 7-230954 (1995) discloses a cleaning technique in which, in a plasma processing apparatus, a residual material attached to a surface of a structural component inside a chamber (process chamber) is heated and thereby decomposed and removed.
Steps for manufacturing a semiconductor component or the like include an ion implantation step of implanting ions of boron, arsenic, or the like, into a silicon wafer (substrate). For the purpose of activating the ions implanted in the substrate, a heat treatment is performed. The heat treatment for activating ions is implemented by heating (annealing) the substrate to a temperature of, for example, about 1000° C. to 1100° C.
In a heat treatment apparatus that performs such a heat treatment, a fault such as a defect or cracking may occur in the substrate due to the heat treatment. For example, in flash annealing that is a heat treatment using flash lamps, the substrate may be broken and a shape fault such as a defect or cracking may occur in the substrate because of an impact caused by instantaneous radiation of light with an enormous amount of energy at a time of flash heating or because the substrate is moved up by a quartz-made arm having a temperature lower than the heat-treated substrate.
A breakage of the substrate causes a large amount of particles in the process chamber due to broken pieces of the substrate itself, damage to peripheral structures, and the like. When a breakage of the substrate occurs, needless to say, the process chamber is opened and maintenance is carried out, for the collection of the broken pieces and the like. However, it is very difficult to completely remove the caused particles. Additionally, opening the process chamber undesirably allows particles existing outside to be newly taken into the process chamber. When the flash heating treatment is performed under a state where particles remain in the process chamber, the particles are attached to the substrate and cause a process fault.
Conventionally, therefore, a method has been adopted in which, after the process chamber is opened and the maintenance is carried out, the flash heating is performed on a dummy wafer to thereby attach particles to the dummy wafer, and the particles are removed. In more detail, in this method, a particle removal process and a comparison and examination process (“particle test”) are repeated until a measurement result of the particle test becomes equal to or less than a predetermined allowable value. In the particle removal process, particles are attached to the dummy wafer by means of the flash heating. In the comparison and examination process, the dummy wafer is taken out from the process chamber and transported into a measuring apparatus that is separately provided and configured to measure the number of particles attached onto the wafer. Then, the number of particles attached to the dummy wafer is measured, and the measurement result is compared and examined against the predetermined allowable value. However, to reach a state where the measurement result of the particle test is equal to or less than the predetermined allowable value, normally, it is necessary to repeat the particle removal process and the particle test a considerable number of times. Moreover, it is normally not easy to perform the particle test in, for example, a user's manufacturing plant in which the heat treatment apparatus is installed. Accordingly, a cleaning process for cleaning the inside of the process chamber after the maintenance requires a considerable number of dummy wafers and a process time, which causes a problem of a large cost increase.
Therefore, in a heat treatment apparatus disclosed in U.S. Pat. No. 7,068,926, a method is adopted in which a particle removal process for removing particles existing in a process chamber is implemented by repeating emission of flashes of light in an empty process chamber having no wafer, to thereby cause particles to scatter within the process chamber, and then exhausting the process chamber. In this method, when the number of times of emission of flashes of light, which is repeated at predetermined time intervals, reaches a predetermined value, it is determined that the number of particles in the process chamber becomes equal to or less than an allowable limit. Thus, the emission of flashes of light process is stopped. Then, similarly to the conventional method, the particle test is performed by actually using a dummy wafer. Based on a result of the particle test, whether or not the cleaning process for cleaning the inside of the process chamber is completed is determined.
However, in the apparatus disclosed in U.S. Pat. No. 7,068,926, it is determined that the number of particles existing in the process chamber becomes equal to or less than the allowable limit, based on the fact that the number of times the flash heating is performed in the empty process chamber reaches a predetermined value. Accordingly, in a case where the number of particles in the process chamber is larger than assumed, the particle test using the dummy wafer is performed under a state where the inside of the process chamber has not been sufficiently cleaned. As a result, the particle removal process using the flash heating and the particle test using the dummy wafer have to be performed again. In this manner, the apparatus disclosed in U.S. Pat. No. 7,068,926 still involves a problem that repetition of the particle test may result in the need for a considerable number of dummy wafers and a process time.
Moreover, conventionally, a situation sometimes occurs in which, in the course of continuously performing the heat treatment on a lot including a plurality of substrates, the degree of cleanliness in the process chamber rapidly deteriorates. A conceivable cause of the deterioration in the degree of cleanliness is, for example, the bringing-in of particles by the substrates or a trouble occurring in a gas supply and exhaust system for supplying and exhausting a gas to and out of the process chamber. Here, in the conventional heat treatment apparatus, even though the degree of cleanliness in the process chamber deteriorates during the process, detection thereof is difficult. Thus, the deterioration cannot be promptly responded to, and there is a fear that a large number of mis-processed substrates may be produced. Additionally, in a case where the degree of cleanliness in the process chamber deteriorates during the process, it is necessary to open the process chamber and carry out the maintenance. This causes a problem of a prolonged downtime.